Sibling studies
by wolfypuppypiles
Summary: Clary watches Alec and Izzy to try and figure out how a sister and brother are supposed to act around each other. But they're confusing to say the least. (Second chapter gets dark yo)
1. Chapter 1

Clary had never had any siblings. Simon was her best friend, and they'd grown up together, so he was kind of like her brother, but it wasn't the same. Now she had a brother, but they'd only known each other for a few weeks and their relationship was more than a little… awkward and confusing.

She had no idea how she was supposed to act around him and it was bad enough that they'd kissed. It was all so confusing and she decided she should probably do some research about how siblings worked.

Simon and his sister had always been around but she'd never had to analyse their behavior and now Simon couldn't see his sister. So, she could look to them as a guideline. So, she was left with Alec and Izzy, but they were confusing.

Clary could never be sure what was happening between those two, it was like they had their own secret language or something. Sometimes they wouldn't even speak but it was like they had a whole conversation and Clary had briefly wondered if there was a telepathic rune that she hadn't been told about.

Clary had watched the silent conversation carefully and still didn't know what it meant.

Jace had been going over a mission and needed Magnus to open a portal. So, someone would have to call him. Izzy had smiled and given Alec a look to which he had seen and frowned at. Izzy merely smiled wider and raised her eyebrows, tilting her head slightly. Alec frowned harder and threw out his hands as if asking what her problem was. So, Izzy crossed her arms and tilted her head the other way, making Alec roll his eyes and give in.

"Fine. I'll call him, Izzy, just stop. And he's not my boyfriend."

Clary had been severely confused about what had happened. Alec had acted as if she'd been talking aloud through her head tilts. For all she knew, she had been, just at a frequency only Alec could hear. As if that wasn't bad enough they seemed to bounce between having fights and loving each other within the span of ten seconds.

"Alec, would you stop! It's not the same and you won't understand because you've always been Mom's favorite!" Izzy had been so upset that she wouldn't look at her brother and Alec had deflated from his rigid stance, sighing as he studied the floor. But after a few moments he'd started smiling and lent on the table next to Izzy.

"Do you remember that time Mom and Dad went to Idris and left without singing us to sleep? And you insisted you couldn't go to bed until she sang?"

Izzy started smiling too, sad eyes softening and she recalled the story.

"Yeah, so you dragged me to your bed and said it was a cheat. I couldn't sleep in my bed but I could sleep in yours and the monsters would look in my room and think I was gone and leave me alone."

They both laughed and looked at each other with quiet smiles. Clary watched the exchange. No "I'm sorry's" no "I forgive you's" just… a memory? And that had been the end of the fight.

Were all siblings this way? How was she and Jace supposed to do that? She barely understood what he was saying when he was speaking actual words.

Or even worse, they'd be in the middle of a fight and get called to do something.

"You don't ever listen to me? Why don't you trust me?"

"I do trust you Izzy it's just- dammit, I have to go. Jace found that other vamp."

"Fine. Be careful, I love you."

"Love you too." And Alec would kiss her forehead and be gone, leaving Izzy as grumpy as she had been before and they would resume their fight when he got home.

The only thing that seemed to be stay constant was the love they both had for each other. It was unconditional and never ending.

Alec could be mad at any of his siblings and still stick up for them at any given moment. Clary had thought Alec would do that in battle, sure, and for his Parabatai because they were linked. But Alec always told others off if they spoke badly about his sister, even if he had been doing the same thing three seconds before.

"Hold your tongue or I'll cut it out of you. You don't get to talk about her."

And just a look from Izzy would stop any chatter about her brother and the warlock he'd made out with.

Clary had been especially surprised when Alec, broody, grumpy, perpetually miserable Alec, would smile or become the biggest softie ever, just because it would make his little sister happy.

Izzy had sprained her ankle during a mission and was unable to put any weight on it. So, Alec, without a second thought, had knelt down and ordered her to get on.

"I'll give you a piggy back ride just don't strangle me with your whip."

Izzy had happily climbed on and wrapped her arms around Alec's neck, as he stood and carried her home. Clary hadn't been able to stop laughing as the shadowhunter ordered people around with his sister clinging to his back.

"Move your ass Raj, and I want that seelie found and brought here, unharmed."

"Um, Alec I-"

"That's an order."

The others nodded and went about their business while Alec tried to look stern and grumpy with Isabelle playing with his hair, still on his back.

And then there were the times Alec threw out every piece of shadowhunter training he had, and allowed himself to be almost killed, because he couldn't bear the thought of hurting his sister.

Clary had watched as Izzy crouched over Alec, digging her nails into his chest as she prepared to bury her hand on his chest. And Alec had just pleaded with her. He hadn't been able to shoot a single arrow at her, regardless of how many ways he could take her down without causing any lasting damage, and he hadn't been able to throw any punches either. Because hurting his sister in any way was unthinkable.

So, he lay there with tears in his eyes and waited to die. Clary didn't want to hurt Izzy either but knew that if the demon inside her got free, it would only destroy more people. Clary stabbed Isabelle and killed the demon, and Alec took care of his sister. Even as his shirt grew damp with blood from the claw marks on his chest, he hugged his sister and told her everything was okay.

Clary had even heard Alec lie to Izzy, saying that he was fine, she hadn't hurt him.

It was then that Clary realized Alec and Isabelle would always love each other more than they loved themselves and that Alec would always choose Izzy over anyone else, even his Parabatai if he needed to.

Having an older brother meant having someone to always love and protect you, someone to be proud of you when you beat the ever-living shit out of some gross mundane. Someone that would always be there when you needed them and could always be trusted to be on your side.

Alec may not have been the nicest person but he was a damn good big brother, and he always would be.


	2. Chapter 2

Clary watched in fascination as Alec and Izzy argued.

"You don't have to protect me, I can look after myself!"

"This isn't about whether or not you can handle yourself against them-"

"Which I can!"

"It's about the mission. We don't need to use you as bait when we can track them back to the nest perfectly fine using their heat signatures."

Izzy laughed without humour, her voice hard and furious.

"Are you serious? The other team have been trying that for weeks and its never worked. The only thing that draws them out is-"

Alec continued rune-ing his arrows, refusing to look at her as he spoke.

"Girls. I know. These demons prefer to steal girls and assume their appearance in order to infiltrate mundane areas. And I will not use you as bait."

Izzy sighed and snatched an arrow from his hand.

"I'll be fine, the last team used one-"

Alec finally looked at her with hard eyes.

"And she was killed. You aren't going, that's an order."

Izzy threw his arrow down with a yell, impaling it into one of the training mats as she stormed out of the room. Clary watched from her hiding spot as Alec sighed and leant on the table, closing his eyes.

He looked exhausted and Clary briefly wondered if she should just leave, before Alec called her out.

"Clary, I know you're there. Grab your stuff we leave in ten."

The girl startled before recovering herself and slowly stepping out of the alcove she'd been hiding in.

"Why am I going? I thought you told Izzy it was too dangerous?"

Alec picked up his bow and quiver, slinging them over his shoulder.

"For her. You'll be fine, Jace and I will be there the whole time. Now get moving we don't have very long."

Clary had been confused and beyond scared to be used as bait for a shapeshifting demon. Jace hadn't been happy about Clary being the one to use as bait but hadn't argued when Alec explained the fight he and Izzy had. He seemed to understand something in the story that Clary hadn't picked up on but she didn't have long to think about it.

The demon showed up to the alley she was milling around in and quickly snatched her in its slimy arms and took her away. It moved so fast she felt as if she would be sick, and they quickly arrived at its dark hole of a home, where it dumped her on the floor and then assumed her appearance.

The hole smelt like rot and wet garbage and she realized why when other demons emerged from the dark. There were so many of them.

They all began shifting and groaning as they began to rip their skin apart to become other versions of herself. She would have screamed if Alec and Jace hadn't torn through the make shift door to rescue her.

Jace held a witch light and squinted through the dark as he yelled.

"Clary? Where are you?"

"I'm here!" But all the demons, now looking exactly like her, said the same thing.

Alec and Jace began surging forward, kicking them down as they cried out in mimicked versions of her own voice, and slicing into their arms or any skin they could get to. It was a messy and heart wrenching process.

Alec grabbed a demon-Clary and held her down as she cried, making a small cut on her arm with his seraph blade. If the skin sizzled and black blood flowed, he would know it was a fraud and kill it before it's angry teeth sunk into his neck.

Jace did the same and the looks on their faces weren't the same focus or glee that were usually there during battle. It was awful work, hurting things that looked and sounded like someone you loved. No wonder Alec had refused to let Izzy come along.

Once they were all dead Jace approached the real Clary as she sat in a corner, curled into a ball, and staring, horrified at the piles of dead versions of herself.

Jace knelt beside her and gently took her arm, apologizing as he brought his blade down on her. It was only a small cut but Clary flinched and swore all the same. Red blood, dripped down her skin and Jace quickly apologized and drew an iratz, pulling her into a hug once the cut began to heal.

"I'm so sorry, but we had to be sure it was really you."

Alec was pulling the bodies into a pile to burn, face a cold mask of indifference.

Jace looked over his shoulder where Clary was watching.

"These demons don't turn back once they die. That's why they're so hard to deal with. We don't have to stay for this, we can get someone else to burn them."

Clary took his hand as he helped her up from the ground, wrapping his jacket around her shaking shoulders.

"Is Alec okay?"

Jace nodded, though he watched his brother with sad eyes.

"Yeah, he and Izzy had a fight about this mission."

"Yeah, he said we were going to use their heat signatures to find the demons. He didn't want to use her as bait but he used me? Why?"

Jace looked at her, an apologetic look on his face.

"It's not like this was easy for either of us, killing those things while they looked like you, cried like you? It's horrible. But if it had been Izzy… he couldn't have done it. Neither of us could have."

Clary felt stupid for not realizing sooner. Of course, Alec hadn't wanted Izzy to come. He'd never be able to hurt his little sister, let alone killing a whole horde of her. Even knowing it was a demon would not have made it any easier to kill things that looked and sounded like his baby sister.

Once the pile of her bodies had been made, Alec came to check she was okay, before they called another group of shadowhunters to do the clean-up while they went back to the institute. Jace held Clary's hand the whole way back, looking as if he wanted to throw up every time he noticed a new patch of blood on himself, while Alec walked ahead, face as cold as stone.

When they finally got back to the institute Izzy was there waiting for them with a furious expression. Alec ran towards her as soon as he saw her, scooping her into his arms and holding her in a tight hug.

"Alec? I'm still mad at you. And you took Clary instead of me?"

Alec didn't say anything, just pressed his face to his sister's neck and gripped her tighter until she put her arms around him and hugged him back. Jace nodded to Izzy, a silent message in his eyes that she seemed to understand when she noticed the slow healing cut on Clary's arm.

"Oh Alec."

That had been the end of their fight. Alec released Izzy so that she could check him over and make sure he was okay before she did the same to Jace and Clary.

Clary saw Alec differently after that. She had always thought he didn't really care, or that he could out shadow hunting before anything else, but really Alec would always be a big brother before anything else. His siblings came first. Before himself, before his job, before everything.


End file.
